Fluorescent lamps in the past have been energized by coil and core ballasts which supply energy to the lamps at the same low frequency alternating current (AC) as the power being supplied to the ballast. These conventional ballasts exhibit several major disadvantages: poor efficiency, wasting electrical energy in the form of heat, no adjustment of light output, poor regulation of light output with varying input voltage, possible audible hum, some light output flicker, and poor power factor load to the source of the AC power.
Modern electronic ballasts offer advantages over the conventional coil and core ballasts but still have certain limitations and in addition introduce at least one additional disadvantage. Existing electronic ballasts operate on essentially the same principle as coil and core ballasts except that the low frequency alternating, drive is converted to a high frequency drive. Regulation of drive to the lamps is limited in both cases, but not controlled. High frequency electronic ballasts offer good efficiency, eliminate audible hum, eliminate flicker, and may provide moderate input factor, however they do not offer improvement in light regulation with AC power line variations, offer no control of light output, and introduce significantly greater radio frequency emissions.
Accordingly it is desirable to have a new and improved circuit for providing power to the fluorescent lamp and substantially eliminating all of the prior problems.